Diblock polyampholytes grafted onto spherical particles : Monte Carlo simulation and lattice mean-field theory

Spherical brushes composed of diblock polyampholytes (diblock copolymers with oppositely chargedblocks) grafted onto solid spherical particles in aqueous solution are investigated by using the primitivemodel solved with Monte Carlo simulations and by lattice mean-field theory. Polyampholyte chains of twocompositions are considered: a copolymer with a long and a short block, A100B10, and a copolymer withtwo blocks of equal length, A50B50. The B block is end-grafted onto the surface, and its charge is varied,whereas the charge of the A block is fixed. Single-chain properties, radial and lateral spatial distributionsof different types, and structure factors are analyzed. The brush structure strongly depends on the chargeof the B block. In the limit of an uncharged B block, the chains are stretched and form an extendedpolyelectrolyte brush. In the other limit with the charges of the blocks compensating each other, the chainsarecollapsedandformapolyelectrolytecomplexsurroundingtheparticles.Atintermediatechargeconditions,a polyelectrolyte brush and a polyelectrolyte complex coexist and constitute two substructures of thespherical brush. The differences of the brush structures formed by the A100B10 and A50B50 polyampholytesare also analyzed. Finally, a comparison of the predictions of the two theoretical approaches is made